Pump construction



United States Patent 3,120,789 PUMP CONSTRUCTlON Erik W. Anthon, Kensington, Califi, assignor to Research Specialties Co., Richmond, Calif., a corporation of California Filed May 29, 1961, Ser. No. 113,193 2 Claims. (Cl. 92-206) This invention relates to improvements in a pump construction and more particularly to positive displacement pumps having a piston moving axially in a bore.

These pumps often resemble the hypodermic syringes in that a plunger is used to actuate the piston and liquids are conveyed into and out of the barrel through tubular members. The present pump construction is particularly adapted for transferring liquids in an automatic chemical analysis apparatus of the character set forth in my copending application Serial No. 61,206 for Materials Handling Apparatus filed October 7, 1960.

in apparatus of this type the pump must be capable of transferring precise volumetric quantities of liquids such as samples, reagents, distilled water, etc. This gives rise to two principal requirements in the construction of the piston and barrel, namely (1) the volume of the pump chamber must remain constant and accordingly wear must be reduced to an absolute minimum; (2) the piston must effect a very good seal with the inner surface of the barrel and at the same time be freely movable.

The materials handling apparatus of my co-pending application, referred to above, performs repetitive analyses upon a large number of samples, and accordingly the liquid transfer pumps are called upon to cycle through a tremendous number of pumping strokes without attention or replacement of parts. Previously known materials and construction have proved to be inadequate for this purpose and, in order to overcome the wear problem, etc. the pump construction of the present invention was conceived and perfected.

Accordingly it is an object of the present invention to provide a syringetype pump construction which is adapted for transferring a wide variety of liquids in precise quantities without contamination of the liquids or appreciable changes in the volumetric capacity of the pumps.

Another object of the invention is to provide a pump construction of the character descrmibed in which the piston provides an excellent seal with the inner surface of the pump chamber while at the same time being self-lubricating so as to be freely movable by the pump actuating mechanism.

A further object of the invention is to provide in a pump construction of the character described a piston construction in which the contact pressure of the piston with the bore is automatically maintained at a desired level.

A still further object of the invention is to provide a skirted piston for a syringe-type pump which is formed of a resilient plastic material having a low coefiicient of friction with the pump bore.

Another object of the invention is to provide a spreading device for resiliently urging the skirt of a piston outwardly into contact with the inner surface of the pump bore with a controlled amount of pressure.

=Further objects and advantages of my invention will be apparent as the specification progresses, and the new and useful features of my pump construction will be fully defined in the claims attached hereto.

The preferred form of my invention is illustrated in the accompanying drawing forming part of this application, in which FIGURE 1 is a side elevational view of a pumping apparatus incorporating the pump construction of the present invention;

FIGURE 2, a cross-sectional view taken substantially on the plane of line 2-2 of FIGURE 1; and

FIGURE 3, an enlarged cross-sectional view of the pump plunger and piston assembly taken substantially on the plane of line 33 of FIGURE 2.

While I have shown only the preferred form of my invention, it should be understood that various changes or modifications may be made within the scope of the claims attached hereto without departing from the spirit of the invention.

Referring to the drawings in detail, it will be seen that the pump construction of the present invention consists basically of a pump barrel 11 having a cylindrical inner surface 12, a plunger 13 axially reciprocable in the barrel 11, an expandable skirt 14 mounted on the plunger 13, and means 16 on the plunger formed for resiliently urging the skirt 14 radially outwardly into sliding contact with the inner surface 12 of the pump barrel.

in accordance with the present invention the pump barrel 11 is highly resistant both to wear and to corrosive effects of the liquids being pumped. 'For this purpose I prefer to use glass or stainless steel, although it should be appreciated that other materials possessing the required characteristics may be employed.

As here shown, the barrel 11 is mounted in a protective housing 17 by means of resilient end blocks 18 and 19. For ease of disassembly to permit cleaning, a cupshaped retainer 241 is releasably mounted on the lower end of the housing 17 by means of set screws 22 engaging in a groove 23 in the housing.

:The sample or other liquid material is conveyed into the pump chamber 24 by any suitable means such as a tube 26 releasably secured to the end block 19 and sealed by means of O-rings 27. The end block 19 is releasably sealed to the lower end of barrel 11 by an O-ring 28.

The plunger 13 extends upwardly through the end of barrel 11 and may be reciprocated by any suitable means such as a laterally extending pin 29 adapted for engagement and vertical reciprocation by the mechanism of my aforesaid copending application. lAD. extension 31 of the housing 17 surrounds the upper end of the plunger and is provided with a slot 32 adapted to maintain the pin 29 in the same circumferential. position during its vertical movement.

The piston skirt 14 is formed of resilient material so that its rim 33 may be forced outwardly into sliding contact with the inner surface 12 of the pump barrel. This outward displacement of the rim 33 is accomplished by a spreading member 34 having a frusto-conical portion proportioned to force the rim 33 outwardly when the member 34 is drawn axially into the skirt 14.

As here shown, the plunger 13 is of hollow construction and a rod 37 is mounted for axial reciprocation therein, the lower end of the rod 37 being secured to the spreading member 34 so that upward movement of the rod relative to the plunger 13 will tend to spread the piston skirt 14.

In accordance with the present invention and as an important feature thereof, the piston skirt 14 is quite thin and is formed of a resilient low-friction plastic ma terial. This material should be highly resistant to corrosive effects of the fluid being pumped and should possess a very low coefiicient of friction. Suitable materials include Teflon (polytetrafiuoroethylene) and. nylon. But, because of its self-lubricating qualities and chemical inertness, I prefer to use Teflon for the piston skirt 14.

As an important feature of the invention, the means 1 6 exerts a controlled resilient spreading action upon the skirt 14 and makes it possible to maintain the desired pressure of the skirt against the bore surface 12 over an extremely long operating life. This is accomplished by spring means 38 carried by the plunger 13 and acting to draw the spreader member 34 into the skirt 14. Preferably and as here shown, the spring means 38 is in the form of a helical spring surrounding the rod 3'7 and compressed between a shoulder 39, carried on rod 37, and the confronting upper end 41 of the plunger 13.

Control over the amount of expansive force being exerted on the piston skirt 14 is provided by forming the shoulder 39 on a nut 42 threaded on the upper end 4.3 of the rod 37. Tightening down of the nut 42 will further compress spring 38, causing it to exert more pulling force on the member 34 with a resultant increase in the outward pressure exerted on the piston skirt rim 33. Backing off of the nut 42 will reduce the expansive force on rim 33. Accordingly, the nut 42 may be adjusted in such manner as to force rim 33 outwardly with a pressure just sufiicient to accomplish a good seal but not suificient to create excess wear.

From the foregoing it will be seen that I have provided a novel syringe-type pump construction well adapted for constant repetitive transfer of precise quantities of a wide variety of liquids and which possesses highly desirable wear characteristics not previously obtainable in apparatus of this nature.

I claim:

1. A syringe-type pump, comprising a pump barrel having a cylindrical inner surface, a hollow plunger axially reciprocable in said barrel, a thin substantially cylindrical Wall of resilient low-friction plastic providing a piston skirt secured to and extending axially from an end of said plunger within said barrel to terminate in a rim, the said rim of said skirt being beveled inwardly, a rod mounted for axial reciprocation in said hollow plunger and having an end extending therefrom, a spreading member secured to the inner end of said rod and having a frusto-conical portion complementary to the beveled rim of said skirt, the outer end of said rod being provided with a shoulder spaced from the adjacent end of said plunger, and spring compressed between said shoulder and the confronting end of said plunger, said 4 spring being formed to resiliently force said spreading member against said skirt whereby said frusto-conical portion Will engage the beveled rim of said skirt so as to force the skirt radially outwardly into sliding contact with the inner surface of the pump barrel.

2. A syringe-type pump, comprising a pump barrel having a cylindrical inner surface, a hollow plunger axially reciprocable in said barrel, a thin substantially cylindrical wall of resilient low-friction plastic providing a piston skirt secured to and extending axially from an end of said plunger within said barrel to terminate in a rim, the said rim of said skirt being beveled inwardly, a rod mounted for axial reciprocation in said hollow plunger and having an end extending therefrom, a spreading membcr secured to the inner end of said rod and having a frusto-conical portion complementary to the beveled rim of said skirt, a nut threaded on the outer end of said rod and formed to provide a shoulder spaced from the adjacent end of said plunger, and a spring compressed between said shoulder and the confronting end of said plunger, said spring being formed to resiliently force said spreading member against said skirt whereby said frusto-conical portion will engage the beveled rim of said skirt so as to force the skirt radially outwardly into sliding contact with the inner surface of the pump barrel, said nut being formed for adjusting the amount of compression on said spring so as to regulate the pressure with which said spreading member is urged into said skirt and thus control the amount of force with which said skirt is forced radially outwardly into sliding contact with the inner surface of said barrel.

References Cited in the file of this patent UNITED STATES PATENTS 858,647 Durkee et al July 2, 1907 1,018,517 'Ohmstede Feb. 27, 1912 1,346,652 Hinshaw et a1. July 13, 1920 1,945,151 Marsh Ian. 30, 1934 2,857,184 Mancusi Oct. 21, 1958 

1. A SYRINGE-TYPE PUMP, COMPRISING A PUMP BARREL HAVING A CYLINDRICAL INNER SURFACE, A HOLLOW PLUNGER AXIALLY RECIPROCABLE IN SAID BARREL, A THIN SUBSTANTIALLY CYLINDRICAL WALL OF RESILIENT LOW-FRICTION PLASTIC PROVIDING A PISTON SKIRT SECURED TO AND EXTENDING AXIALLY FROM AN END OF SAID PLUNGER WITHIN SAID BARREL TO TERMINATE IN A RIM, THE SAID RIM OF SAID SKIRT BEING BEVELED INWARDLY, A ROD MOUNTED FOR AXIAL RECIPROCATION IN SAID HOLLOW PLUNGER AND HAVING AN END EXTENDING THEREFROM, A SPREADING MEMBER SECURED TO THE INNER END OF SAID ROD AND HAVING A FRUSTO-CONICAL PORTION COMPLEMENTARY TO THE BEVELED RIM OF SAID SKIRT, THE OUTER END OF SAID ROD BEING PROVIDED WITH A SHOULDER SPACED FROM THE ADJACENT END OF SAID PLUNGER, AND SPRING COMPRESSED BETWEEN SAID SHOULDER AND THE CONFRONTING END OF SAID PLUNGER, SAID SPRING BEING FORMED TO RESILIENTLY FORCE SAID SPREADING MEMBER AGAINST SAID SKIRT WHEREBY SAID FRUSTO-CONICAL PORTION WILL ENGAGE THE BEVELED RIM OF SAID SKIRT SO AS TO FORCE THE SKIRT RADIALLY OUTWARDLY INTO SLIDING CONTACT WITH THE INNER SURFACE OF THE PUMP BARREL. 